The present invention relates to mechanical compliance systems and more particularly to an improved remote center compliance apparatus which is highly useful in the field of automated assembly.
Since the advent of automatic manufacturing systems, interest has existed in automatizing the assembly of parts. For the most part, problems associated with the assembly of close-fitting parts have prevented wide-scale extensions of the current trend toward automated manufacturing from extending into the area of assembly.
One problem which frequently arises in the assembly of close-fitting parts, where the collective tolerances of the parts in assembly equipment exceeds the assembly clearance, is "jamming". Part "jamming" occurs in assembly because a part is not pushed perfectly into its proper location. Once a slight "jam" occurs, pressure applied to the top of the part being located (at the grouping location) most frequently results in even further "jamming". This further "jamming" occurs because the part tends to rotate about the point where pressure is applied.
In the past, attempts have been made to solve the problems of close-fitting assembly with elaborate force feedback electronics sensing devices. In addition to cost considerations, these devices frequently generated ambiguous signals in "jamming" situations, and the resulting correction force did not always free the "jam".
Many of the problems resulting from "jamming" have been ameliorated by mechanical compliance as in the prior art. The most successful of these systems creates a virtual rotational center at or beyond the assembly parts interface. The effect of creating a virtual rotational center at this remote location is similar to the effect of pulling the assembly parts together from the virtual center. This effect is, however, generated by pushing the part on the opposite side of the assembly interface. By effectively moving the rotation center to a point near or beyond the assembly interface, continued pressure applied at the opposite side of the assembly interface will tend to align the parts and alleviate the "jamming".
While effectively pulling parts together results in substantially fewer "jams" than pushing, pulling alone will not eliminate "jamming" problems. One notoriously common example of a "jam" which results from pulling is a drawer which "jams" when pulled from a chest of drawers. The prior art remote center compliance systems have attempted to further correct the small number of pulling type "jams" by superimposing a translational compliance system onto the rotary compliance system created by the remote center. The result has been partially successful in that it does alleviate many pulling type "jams". The translational compliance provides a second uncoupled independent freedom which eliminates the pulling type "jam".
This solution has not been totally successful. The translational compliance makes horizontal assembly most difficult. The mechanical translational compliance apparatus cannot distinquish between gravity and assembly interface forces. Thus, for horizontal assembly applications (as opposed to vertical assembly in which one part is positioned beneath the other), particularly those involving heavy parts or heavy tooling, the prior art remote center compliance systems have become unworkable.
The present invention alleviates many of the problems of existing remote center compliance systems and is particularly advantageous in horizontal assembly applications. The present invention provides two independent freedoms of movement with the remote center "smeared" between two locations.